The recording materials which utilize the coloration caused by the reaction between a coloring dye and a developer allow recording to be attained quickly by a relatively simple apparatus without requiring complicated processes such as, for example, development and fixing. Owing to this advantage, they have been widely used as a thermal printing paper for recording the output of a device such as, for example, a facsimile system or a printer and as a pressure-sensitive copying paper for simultaneously copying a plurality of sheets such as in account slips at a time.
These recording materials are required to generate a color quickly, preserve the whiteness of an uncolored part (hereinafter referred to as "background"), and abound in fastness of a colored image and the background thereof. In recent years, they have come to find utility in large quantities in the field of recorded images such as, for example, labels for which reliability forms an important consideration. Thus, the desirability of providing a recording material possessed of a colored image rich in lasting stability to withstand a plasticizer and oil contained in organic high polymer materials which are used in packages has been finding enthusiastic public recognition. With a view to solving this problem, therefore, various studies have been made for the development of various auxiliaries such as conservatives, let alone coloring dyes and developers. None of the outcomes of these studies, however, have been found to be fully satisfactory.
As close equivalents for the compounds of this invention, diphenyl sulfone derivatives may be cited. These have been known as a developer for use in recording materials. The diphenyl sulfone derivatives which have an alkoxy group or aralkyloxy group as one moiety and a hydroxy group as the other moiety have been proposed in JP-A-57-210,886, JP-A-58-20,493, JP-A-58-82,788, JP-58-132,593, JP-A-60-13,852, and IP-A-W084/02882.
None of them, however, deserve to be called fully satisfactory in terms of stability of the conservation of image mentioned above.
Recently, as means to improve the capacity for conservation under discussion, numerous inventions relating to recording materials which contain the novolak type epoxy resin or the epoxy group of a glycidyl compound have been filed for patent. The present patent applicant himself has filed inventions which relate to 4-hydroxy-4'-(2-methyl glycidyloxy) diphenyl sulfone (IP-A-WO93/06074) and phenetyl alcohol derivatives (IP-A-WO94/07832). These inventions are not yet fully satisfactory for the sake of reduction to practice in terms of cleanliness of background and stability of conservation.
The recording materials, therefore, remain yet to be improved in stability of the conservation of a colored image and, particularly in recent years, in resistance to the plasticizer. It is an object of this invention to provide a recording material which excels in stability of the conservation of a colored image for the purpose of solving the problem in question.